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Title: SU-E-J-170: Dosimetric Consequences of Uncorrected Rotational Setup Errors During Stereotactic Body Radiation Therapy (SBRT) Treatment of Pancreatic Cancers

Abstract

Purpose: To explore the dosimetric consequences of uncorrected rotational setup errors during SBRT for pancreatic cancer patients. Methods: This was a retrospective study utilizing data from ten (n=10) previously treated SBRT pancreas patients. For each original planning CT, we applied rotational transformations to derive additional CT images representative of possible rotational setup errors. This resulted in 6 different sets of rotational combinations, creating a total of 60 CT planning images. The patients’ clinical dosimetric plans were then applied to their corresponding rotated CT images. The 6 rotation sets encompassed a 3, 2 and 1-degree rotation in each rotational direction and a 3-degree in just the pitch, a 3-degree in just the yaw and a 3-degree in just the roll. After the dosimetric plan was applied to the rotated CT images, the resulting plan was then evaluated and compared with the clinical plan for tumor coverage and normal tissue sparing. Results: PTV coverage, defined here by V33 throughout all of the patients’ clinical plans, ranged from 92–98%. After an n degree rotation in each rotational direction that range decreased to 68–87%, 85–92%, and 88– 94% for n=3, 2 and 1 respectively. Normal tissue sparing defined here by the proximal stomach V15more » throughout all of the patients’ clinical plans ranged from 0–8.9 cc. After an n degree rotation in each rotational direction that range increased to 0–17 cc, 0–12 cc, and 0–10 cc for n=3, 2, and 1 respectively. Conclusion: For pancreatic SBRT, small rotational setup errors in the pitch, yaw and roll direction on average caused under dosage to PTV and over dosage to proximal normal tissue. The 1-degree rotation was on average the least detrimental to the normal tissue and the coverage of the PTV. The 3-degree yaw created on average the lowest increase in volume coverage to normal tissue. This research was sponsored by the AAPM Education Council through the AAPM Education and Research Fund for the AAPM Summer Undergraduate Fellowship Program.« less

Authors:
 [1]; ; ; ;  [2]
  1. Chicago, IL (United States)
  2. John Hopkins University, Baltimore, MD (United States)
Publication Date:
OSTI Identifier:
22499280
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; ANIMAL TISSUES; COMPUTERIZED TOMOGRAPHY; ERRORS; IMAGE PROCESSING; IMAGES; NEOPLASMS; PANCREAS; PATIENTS; PLANNING; RADIOTHERAPY; STOMACH

Citation Formats

Di Maso, L, Forbang, R Teboh, Zhang, Y, Herman, J, and Lee, J. SU-E-J-170: Dosimetric Consequences of Uncorrected Rotational Setup Errors During Stereotactic Body Radiation Therapy (SBRT) Treatment of Pancreatic Cancers. United States: N. p., 2015. Web. doi:10.1118/1.4924255.
Di Maso, L, Forbang, R Teboh, Zhang, Y, Herman, J, & Lee, J. SU-E-J-170: Dosimetric Consequences of Uncorrected Rotational Setup Errors During Stereotactic Body Radiation Therapy (SBRT) Treatment of Pancreatic Cancers. United States. doi:10.1118/1.4924255.
Di Maso, L, Forbang, R Teboh, Zhang, Y, Herman, J, and Lee, J. Mon . "SU-E-J-170: Dosimetric Consequences of Uncorrected Rotational Setup Errors During Stereotactic Body Radiation Therapy (SBRT) Treatment of Pancreatic Cancers". United States. doi:10.1118/1.4924255.
@article{osti_22499280,
title = {SU-E-J-170: Dosimetric Consequences of Uncorrected Rotational Setup Errors During Stereotactic Body Radiation Therapy (SBRT) Treatment of Pancreatic Cancers},
author = {Di Maso, L and Forbang, R Teboh and Zhang, Y and Herman, J and Lee, J},
abstractNote = {Purpose: To explore the dosimetric consequences of uncorrected rotational setup errors during SBRT for pancreatic cancer patients. Methods: This was a retrospective study utilizing data from ten (n=10) previously treated SBRT pancreas patients. For each original planning CT, we applied rotational transformations to derive additional CT images representative of possible rotational setup errors. This resulted in 6 different sets of rotational combinations, creating a total of 60 CT planning images. The patients’ clinical dosimetric plans were then applied to their corresponding rotated CT images. The 6 rotation sets encompassed a 3, 2 and 1-degree rotation in each rotational direction and a 3-degree in just the pitch, a 3-degree in just the yaw and a 3-degree in just the roll. After the dosimetric plan was applied to the rotated CT images, the resulting plan was then evaluated and compared with the clinical plan for tumor coverage and normal tissue sparing. Results: PTV coverage, defined here by V33 throughout all of the patients’ clinical plans, ranged from 92–98%. After an n degree rotation in each rotational direction that range decreased to 68–87%, 85–92%, and 88– 94% for n=3, 2 and 1 respectively. Normal tissue sparing defined here by the proximal stomach V15 throughout all of the patients’ clinical plans ranged from 0–8.9 cc. After an n degree rotation in each rotational direction that range increased to 0–17 cc, 0–12 cc, and 0–10 cc for n=3, 2, and 1 respectively. Conclusion: For pancreatic SBRT, small rotational setup errors in the pitch, yaw and roll direction on average caused under dosage to PTV and over dosage to proximal normal tissue. The 1-degree rotation was on average the least detrimental to the normal tissue and the coverage of the PTV. The 3-degree yaw created on average the lowest increase in volume coverage to normal tissue. This research was sponsored by the AAPM Education Council through the AAPM Education and Research Fund for the AAPM Summer Undergraduate Fellowship Program.},
doi = {10.1118/1.4924255},
journal = {Medical Physics},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}
  • Purpose: SBRT shows excellent tumor control and toxicity rates for patients with locally advanced pancreatic cancer (PCA). Herein, we evaluate the feasibility of using VMAT with ABC for PCA SBRT. Methods: Nine PCA patients previously treated via SBRT utilizing 11-beam step-and-shoot IMRT technique in our center were retrospectively identified, among whom eight patients received 3300cGy in 5 fractions while one received 3000cGy in 5 fractions. A VMAT plan was generated on each patient’s planning CT in Pinnacle v9.8 on Elekta Synergy following the same PCA SBRT clinical protocol. Three partial arcs (182°–300°, 300°-60°, and 60°-180°) with 2°/4° control-point spacing weremore » used. The dosimetric difference between the VMAT and the original IMRT plans was analyzed. IMRT QA was performed for the VMAT plans using MapCheck2 in MapPHAN and the total delivery time was recorded. To mimic the treatment situation with ABC, where patients hold their breath for 20–30 seconds, the delivery was intentionally interrupted every 20–30 seconds. For each plan, the QA was performed with and without beam interruption. Gamma analysis (2%/2mm) was used to compare the planned and measured doses. Results: All VMAT plans with 2mm dose grid passed the clinic protocol with similar PTV coverage and OARs sparing, where PTV V-RxDose was 92.7±2.1% (VMAT) vs. 92.1±2.6% (IMRT), and proximal stomach V15Gy was 3.60±2.69 cc (VMAT) vs. 4.80±3.13 cc (IMRT). The mean total MU and delivery time of the VMAT plans were 2453.8±531.1 MU and 282.1±56.0 seconds. The gamma passing rates of absolute dose were 94.9±3.4% and 94.5±4.0% for delivery without and with interruption respectively, suggesting the dosimetry of VMAT delivery with ABC for SBRT won’t be compromised. Conclusion: This study suggests that PCA SBRT using VMAT with ABC is a feasible technique without compromising plan dosimetry. The combination of VMAT with ABC will potentially reduce the SBRT treatment time.« less
  • Purpose: To assess the feasibility of treating lung SBRT patients with the ipsilateral arm adducted beside the body instead of elevated above the head. Methods: Patients receiving lung SBRT at our institution are typically treated with both arms raised above their head. However, several patients had difficulty maintaining their arms in an elevated position. In this study, lung SBRT patients who underwent PET-CT imaging with an adducted ipsilateral arm were selected to investigate the dosimetric effects of this treatment setup. PET-CT datasets were fused with treatment planning CT images to simulate the adducted arm position. One VMAT treatment plan wasmore » created per patient using the Pinnacle treatment planning system. Plans were optimized to achieve minimal dose to the ipsilateral arm while keeping the target coverage and critical structure doses within clinical limits. The target dose coverage, conformity index (CI) for the target, and DVHs of critical structures for the adducted arm plan were calculated. These parameters were compared with the clinical plan and reported along with the mean and maximum doses of the ipsilateral arm. Results: The target coverage, CI and DVHs for the adducted arm plans of two patients (one with peripheral lesion and one with central lesion) were comparable with the clinical plans. Dose constraints for the chest wall limited further reduction of ipsilateral arm doses for the peripheral lesion plan. The mean ipsilateral arm doses for the central and peripheral lesions were 0.33 Gy and 2.4 Gy, respectively. The maximum ipsilateral arm doses for the central and peripheral lesions were 1.0 Gy and 6.2 Gy, respectively. Conclusion: The results suggested patients with central lung SBRT tumors were more suitable for treatment with the adducted arm position. More patients with various lung tumor locations will be studied to find optimal tumor locations for treatment with this arm position.« less
  • Purpose: Delineation of gross tumor volumes (GTVs) is important for stereotactic body radiotherapy (SBRT). However, tumor volume changes during treatment response. Here, we have investigated tumor volume changes and movement during SBRT for lung cancer, as a means of examining the need for adaptive radiation therapy (ART). Methods: Fifteen tumors in 15 patients with lung cancer were treated with SBRT (total dose: 60 Gy in 4 fractions). GTVs were obtained from cone-beam computed tomography scans (CBCT1–4) taken before each of the 4 fractions was administered. GTVs were delineated and measured by radiation oncologists using a treatment planning system. Variance inmore » the tumor position was assessed between the planning CT and the CBCT images. To investigate the dosimetric effects of tumor volume changes, planning CT and CBCT4 treatment plans were compared using the conformity index (CI), homogeneity index (HI), and Paddick’s index (PCI). Results: The GTV on CBCT1 was employed as a baseline for comparisons. GTV had decreased by a mean of 20.4% (range: 0.7% to 47.2%) on CBCT4. Most patients had smaller GTVs on CBCT4 than on CBCT1. The interfractional shifts of the tumor position between the planning CT and CBCT1–4 were as follows: right-left, −0.4 to 1.3 mm; anterior-posterior, −0.8 to 0.5 mm; and superiorinferior, −0.9 to 1.1 mm. Indices for plans from the planning CT and CBCT4 were as follows: CI = 0.94±0.02 and 1.11±0.03; HI= 1.1±0.02 and 1.10±0.03; and PCI = 1.35±0.16 and 1.11±0.02, respectively. Conclusion: CI, HI, and PCI did not differ between the planning CT and CBCTs. However, daily CBCT revealed a significant decrease in the GTV during lung SBRT. Furthermore, there was an obvious interfractional shift in tumor position. Using ART could potentially lead to a reduced GTV margin and improved regional tumor control for lung cancer patients with significantly decreased GTV.« less
  • Purpose: This study evaluates the dosimetric differences using volumetric modulated arc therapy (VMAT) in patients previously treated with intensity modulated radiation therapy IMRT for stereotactic body radiotherapy (SBRT) in early stage lung cancer. Methods: We evaluated 9 consecutive medically inoperable lung cancer patients at the start of the SBRT program who were treated with IMRT from November 2010 to October 2011. These patients were treated using 6 MV energy. The 9 cases were then re-planned with VMAT performed with arc therapy using 6 MV flattening filter free (FFF) energy with the same organs at risk (OARS) constraints. Data collected formore » the treatment plans included target coverage, beam on time, dose to OARS and gamma pass rate. Results: Five patients were T1N0 and four patients were T2N0 with all tumors less than 5 cm. The average GTV was 13.02 cm3 (0.83–40.87) and average PTV was 44.65 cm3 (14.06–118.08). The IMRT plans had a mean of 7.2 angles (6–9) and 5.4 minutes (3.6–11.1) per plan. The VMAT plans had a mean of 2.8 arcs (2–3) and 4.0 minutes (2.2–6.0) per plan. VMAT had slightly more target coverage than IMRT with average increase in D95 of 2.68% (1.24–5.73) and D99 of 3.65% (0.88–8.77). VMAT produced lower doses to all OARs. The largest reductions were in maximum doses to the spinal cord with an average reduction of 24.1%, esophagus with an average reduction of 22.1%, and lung with an average reduction in the V20 of 16.3% The mean gamma pass rate was 99.8% (99.2–100) at 3 mm and 3% for VMAT with comparable values for IMRT. Conclusion: These findings suggest that using VMAT for SBRT in early stage lung cancer is superior to IMRT in terms of dose coverage, OAR dose and a lower treatment delivery time with a similar gamma pass rate.« less
  • Purpose: To characterize the dosimetric effects of field aperture margin design in Stereotactic Body Radiation Therapy (SBRT). Methods: Three artificial spherical PTVs, with diameter of 10mm, 20mm and 30mm, were created on CT images of a human body thoracic phantom. Seven non-coplanar isocentric fields were used for treatment planning. For each PTV, treatment plans with margins 0mm, 1mm, 2mm and 3mm were planned. Dosimetric comparison among plans was done considering the following parameters: prescribed isodose line for target coverage, maximum dose, mean dose as well as dose spillages of V80, V50, and V20. Results: Corresponding to aperture margins of 0mm,more » 1mm,2m and 3mm used in the treatment planning, the percentage of isodose line chosen for dose prescription increases from 65% to 93% for 10mm PTV, 70% to 92% for 20mm PTV, and 75% to 92% for 30mm PTV. The maximum dose decrease accordingly from 155.7% to 109.5% for 10mm PTV, 145% to 111.6% for 20mm PTV, 137% to 112.2% for 30mm PTV. The mean dose decrease from 138.% to 104.4% for 10mm PTV, 122.8% to 106.1% for 20mm PTV, 121.3% to 106% for 30mm PTV. Dose spillages (mm3) increase (V80−2.6 to 4.02, V50−4.55 to 9.3, V20–87.86 to 101.71) for 10 mm PTV, (V80−6.78 to 9.89, V50–13.46 to 20.4, V20-119.16 to 219.1) for 20 mm PTV, (V80–22.01 to 28.59, V50–41.56 to 52.66, V20-532.71 to 551.84) for 30 mm PTV. Conclusion: In SBRT treatment planning, tight field aperture margin requires prescribing dose to lower isodose line that leading to higher dose inhomogeneity and higher mean dose to PTV. Loose margin allows prescribing dose to higher isodose line, therefore improves the dose homogeneity. However, it increases dose spillages. Clinician could try different margins according to the PTV size and location of surrounding critical organs to optimize the dose delivered to the patient.« less